1. Field of Invention
The present invention is directed generally to image-guided medical procedures, and more particularly, to instrumentation for the optimal placement of multiple surgical implements using image-based surgical guided navigation systems.
2. Description of the Related Art
Many surgical procedures include a surgeon placing multiple implements within a patient's body. Some of these procedures dictate implement placement in a specific geometry to maximize the effectiveness of the treatment. Certain factors, such as the characteristics of the patient's anatomy, can also influence the desired relative placement of the multiple implements. Some procedures place the implements at a specified angle relative to each other, while others may use a parallel arrangement. One such procedure which utilizes a parallel configuration is the fixation of a femoral neck fracture. Typically, this type of fracture is stabilized utilizing three parallel cannulated screws. Each screw is placed perpendicularly to the fracture site and in such a manner that the distance between each screw is equal, thus forming an equilateral triangle. Parallel placement of the screws is desired so that the bones are properly pulled together. If the screws are not placed in such a parallel manner, shearing forces at the fracture site can prevent proper healing. Furthermore, the triangular screw arrangement increases the stability of the fracture fixation and prevents rotation between the bone fragments. Studies have suggested that three screws are an optimal number since additional implements provide no strength advantage and additional screw penetration increases risk. Femoral neck fracture stabilization using this method can be performed percutaneously while the patient is under regional anesthesia, thus reducing risk associated with more invasive procedures.
Traditional techniques to accurately position and orient implements have included the use of x-ray images to localize the position of the implement tool guide. Through the continuous acquisition of x-ray images during the medical procedure, real-time placement of the tool guide relative to the patient's anatomy can be displayed. More recently, fluoroscopically-based surgical navigation systems have been employed for tool guide positioning by tracking the tool and superimposing its representation onto pre-acquired images without requiring x-rays to be continually taken during the actual surgical procedure.
Current practice for multiple implement placement utilizing image-based surgical navigation systems typically employs tracked guides which contain a single cannula. As used herein, the term cannula refers to a tubular member having at least one hollow channel (i.e., lumen), for insertion in and/or placement adjacent to a patient's body. Such an instrument could be used to place implements in and/or adjacent to a patient by positioning the cannula in the region of interest, and then placing the implement in the region by means of the channel. As used herein, the term implement refers to a surgical tool or device for performing medical procedures. An implement could be a drill, a guide wire, or implants such as screws, nails, etc.
Those skilled in the art should recognize that there are many different types of cannulas and many different ways in which cannulas could be used. For example, a cannula could be rigid, semi-rigid, or flexible and could be configured in any number of different forms, such as a catheter, needle, endoscope, implement inserter, etc.
Utilizing a single cannula means the surgeon typically will position each implement individually. The procedure usually starts by attaching a reference tracking frame to the surgical anatomy. X-ray images are then taken utilizing a fluoroscopic imager which is also tracked by the navigation system. The surgeon then positions the tracked guide for the first implement with the aid of the navigational system display. Once the tool guide is properly positioned, the cannula is used to place the guide wire and subsequent implement into the desired anatomical site. The next implement is then placed relative to the first, and so on. In order for the surgeon to properly place the subsequent implement relative to the previous, new images are taken with the previous implement in place.
One difficulty of the current practice is in achieving relative accuracy of the implement placement. To achieve the desired relative implement geometry, the surgeon estimates each trajectory individually based upon the prior implements. Thus, the relative accuracy is based on the physician's estimate. Furthermore, each implement may involve generating a new set of images of the patient's anatomy before the subsequent implement can be placed, which can increase the time of the procedure and radiation exposure to both the patient and operating room personnel.